tabpage_S: Name tp_localdir per convention.

src/nvim/buffer_defs.h

@@ -825,8 +825,7 @@ struct tabpage_S {
   frame_T         *(tp_snapshot[SNAP_COUNT]);    ///< window layout snapshots
   dictitem_T tp_winvar;             ///< variable for "t:" Dictionary
   dict_T          *tp_vars;         ///< internal variables, local to tab page
-  char_u          *localdir;        ///< Absolute path of local directory or
-                                    ///< NULL
+  char_u          *tp_localdir;     ///< Absolute path of local CWD or NULL
 };
 
 /*